Alterations in local cerebral glucose utilization during electrical stimulation of the striatum and globus pallidus in rats

Position and Orientation Insensitive Wireless Power Transmission for EnerCage-Homecage System

We have developed a new headstage architecture as part of a smart experimental arena, known as the EnerCage-HC2 system, which automatically delivers stimulation and collects behavioral data over extended periods with minimal small animal subject handling or personnel intervention in a standard rodent homecage. Equipped with a four-coil inductive link, the EnerCage-HC2 system wirelessly powers the receiver (Rx) headstage, irrespective of the subject's location or head orientation, eliminating the need for tethering or carrying bulky batteries. On the transmitter (Tx) side, a driver coil, five high-quality (Q) factor segmented resonators at different heights and orientations, and a closed-loop Tx power controller create a homogeneous electromagnetic (EM) field within the homecage 3-D space, and compensate for drops in power transfer efficiency (PTE) due to Rx misalignments. The headstage is equipped with four small slanted resonators, each covering a range of head orientations with respect to the Tx resonators, which direct the EM field toward the load coil at the bottom of the headstage. Moreover, data links based on Wi-Fi, UART, and Bluetooth low energy are utilized to enables remote communication and control of the Rx. The PTE varies within 23.6%-33.3% and 6.7%-10.1% at headstage heights of 8 and 20 cm, respectively, while continuously delivering >40 mW to the Rx electronics even at 90° rotation. As a proof of EnerCage-HC2 functionality in vivo, a previously documented on-demand electrical stimulation of the globus pallidus, eliciting consistent head rotation, is demonstrated in three freely behaving rats.

Effects of Pharmacological Block of GABA(A) Receptors on Pallidal Neurons in Normal and Parkinsonian State

The globus pallidus plays a central integrative role in the basal ganglia circuitry. Morphological studies have revealed a high level of GABA and GABA_A receptors in the globus pallidus. To further investigate the effects of endogenous GABA_A neurotransmission in the globus pallidus of normal and parkinsonian rats, in vivo extracellular recording and behavioral tests were performed in the present studies. In normal rats, micro-pressure ejection of GABA_A receptor antagonist gabazine (0.1 mM) increased the spontaneous firing rate of pallidal neurons by 28.3%. Furthermore, in 6-hydroxydopamine parkinsonian rats, gabazine increased the firing rate by 46.0% on the lesioned side, which was significantly greater than that on the unlesioned side (21.5%, P < 0.05), as well as that in normal rats (P < 0.05). In the behaving rats, unilateral microinjection of gabazine (0.1 mM) evoked consistent contralateral rotation in normal rats, and significantly potentiated the number of apomorphine-induced contralateral rotations in parkinsonian rats. The present electrophysiological and behavioral findings may provide a rational for further investigations into the potential of pallidal endogenous GABA_A neurotransmission in the treatment of Parkinson's disease.

Electrophysiological and behavioral effects of zolpidem in rat globus pallidus

The globus pallidus is believed to play a critical role in the normal function of the basal ganglia, and abnormal activity of its neurons may underlie some basal ganglia motor symptoms. A high density of benzodiazepine binding sites on GABAA receptors has been reported in the rat globus pallidus. The present study investigates the effect of activating the benzodiazepine site by the agonist zolpidem. In in vitro slices, 100 nM of zolpidem significantly prolonged the half decay time of both miniature and spontaneous inhibitory postsynaptic currents by 30.1 +/- 3.0% (n=12) and 17.8 +/- 2.4% (n=16), respectively, with no effect on their amplitudes and frequencies. In the behaving animal, when zolpidem was microinjected into the globus pallidus unilaterally, it caused a robust ipsilateral rotation (26.4 +/- 2.4 turns/30 min, n=8), significantly higher than that of control animals receiving vehicle injection (1.3 +/- 1.6 turns/30 min, n=6). This effect was in agreement with the in vitro effect of zolpidem in enhancing the action of GABA on postsynaptic GABAA receptors. All the effects of zolpidem, in vitro or in vivo, were sensitive to the benzodiazepine antagonist flumazenil, confirming the specificity on the benzodiazepine site. This finding on the effect of zolpidem on motor behavior provides a rationale for further investigations into its potential in the treatment of motor disorders originating from the basal ganglia.

Rotational behavior and electrophysiological effects induced by GABA(B) receptor activation in rat globus pallidus

GABA is the major neurotransmitter used in the globus pallidus and there is evidence that GABA(B) receptors exist in this nucleus. Here we show that unilateral microinjection of baclofen, a GABA(B) receptor agonist, induced ipsilateral turning in Sprague-Dawley rats. This effect was prevented by preinjection of the GABA(B) receptor antagonist CGP55845A, which itself did not cause rotation. Thus, activation of GABA(B) receptor may suppress the activity of globus pallidus neurons, which is in line with the finding that the glutamate receptor antagonists (+/-)-2-amino-5-phosphonopentanoic acid and 6-cyano-7-nitroquinoxaline-2,3-dione also caused similar ipsilateral turning when injected into globus pallidus. Furthermore, in the presence of these glutamate receptor antagonists, injection of baclofen resulted in fewer rotations. To test the possibility that baclofen reduced glutamate release onto globus pallidus neurons, the effects of baclofen on miniature excitatory postsynaptic currents were studied in rat brain slices. Patch-clamp recordings showed that baclofen at 30 microM significantly reduced the frequency of the miniature excitatory postsynaptic currents. However, baclofen induced a weak outward current only in a minority of globus pallidus neurons. These pre- and postsynaptic effects of baclofen were reversed or prevented by CGP55845A. These results suggest that GABA(B) receptor in globus pallidus plays an important role in the regulation of movement by modulating glutamatergic inputs at a presynaptic site.

The effect of the destruction of the caudate-putamen on the development of amygdaloid kindling and kindled seizures

To elucidate the possible roles of the caudate-putamen (CP) on the development of amygdala (AM) kindling and AM-kindled seizures, the bilateral CP were destroyed by intra-CP injection of ibotenic acid (0.5 or 1.0 microg per side) before the AM kindling or after completion of the AM kindling. Prior destruction of the CP, especially by 0.5 microg ibotenic acid injection, caused a significant delay in seizure development. However, after completion of the AM kindling, bilateral destruction of the CP significantly suppressed AM-kindled seizures in proportion to lesion size, however, all animals reached a stage 5 seizure by additional stimulations and established AM kindling. These findings suggest that the intact CP modulates the development of the AM kindling and the generalization and/or expression of the kindled AM seizures, and that the CP plays an important role in the generalization and/or expression of the kindled AM seizures.

Cannabinoid effects in basal ganglia in a rat model of Parkinson's disease

Cannabinoid receptors in the brain are highly concentrated in the basal ganglia, which is in accordance with their well known effects on motor behavior. In this study, rats with 6-hydroxydopamine lesions of the nigrostriatal pathway were implanted with cannulae in the striatum, globus pallidus and substantia nigra. The effect of unilateral infusion of the potent cannabinoid agonist CP55,940 on turning behavior was studied for each structure. Lesioned animals responded to intrapallidal and intrastriatal administration of the cannabinoid in a manner that was similar to that of unlesioned animals. However, lesioned animals showed greater contralateral turning in response to the cannabinoid infusions in the substantia nigra than unlesioned animals.

Effects of intrapallidal cannabinoids on rotational behavior in rats: interactions with the dopaminergic system

The effect of unilateral intrapallidal cannabinoid receptor stimulation on rotational behavior in rats was explored. The potent cannabinoid agonist CP55,940 (5 microg/0.5 microl) induced ipsilateral turning when microinjected unilaterally into the globus pallidus. The D2 dopamine agonist quinpirole reversed this ipsilateral rotation but failed to affect motor behavior on its own. Finally, the D1 dopamine agonist SKF 82958 inhibited movement when administered into the globus pallidus, and this effect was not additive with CP55,940.

The effects of N-methyl-D-aspartate (NMDA) and its competitive antagonist, 3-(2-carboxypiperazine-4-yl)propyl-1-phosphonic acid (CPP), injected into caudate-putamen on kindled amygdaloid seizures in rats

N-methyl-D-aspartate (NMDA) is an agonist of NMDA receptors and 3-(2-carboxypiperazine-4-yl)propyl-1-phosphonic acid (CPP) is an NMDA receptor antagonist. NMDA (1 or 2 nmol per side) or CPP (2.5 or 10 nmol per side) was injected into the bilateral caudate-putamen of amygdaloid-kindled rats. In addition, CPP (10 nmol) was ipsilaterally or contralaterally injected into the unilateral caudate-putamen. Either 20 min after NMDA or 60 min after CPP, the kindled amygdala was stimulated at the generalized seizure triggering threshold. In a few animals tested, injection of NMDA into the bilateral caudate-putamen produced transient spiking activity, with no clinical manifestations. This feature began about 5 min after the injection and lasted about 10 s. When these animals were excluded from the statistical analysis, NMDA in the caudate-putamen showed a weak and non-significant anticonvulsant action. Injection of CPP into the bilateral caudate-putamen caused no ictal change, but markedly suppressed the kindled seizures. Injection of CPP into the unilateral caudate-putamen, regardless of the site, did not cause any ictal change, or affect the stimulation of the amygdala. These findings suggest that: (1) NMDA receptors in the caudate-putamen facilitate the development of kindled amygdaloid seizures; (2) activation of NMDA receptors in the bilateral, but not in the unilateral, caudate-putamen is required for the generalization and expression of kindled amygdaloid seizures.

Effects of 6-hydroxydopamine lesions of the medial prefrontal cortex on local cerebral blood flow and D1 and D2 dopamine receptor binding in rats: a quantitative autoradiographic study

The effects of lesions of the dopamine (DA) nerve terminals in the medial prefrontal cortex (MPFC) on local cerebral blood flow (LCBF) and DA receptor binding in rats were investigated. 4 micrograms of 6-hydroxydopamine (6-OHDA) was infused stereotaxically into the area of the bilateral MPFC of rats pretreated with desmethylimipramine, and control rats received a vehicle solution. Twenty-four days after the operation LCBFs of 23 brain regions were measured using the quantitative autoradiographic N-isopropyl-p-[125I]iodoamphetamine technique D1 and D2 DA receptor binding in various brain regions was also quantified autoradiographically using [3H]SCH 23390 and [3H]YM 09151-2 as the respective ligands. 6-OHDA lesions of MPFC produced significant increases in LCBF of the nucleus accumbens, the dorsolateral portion of the caudate-putamen and the anterior cingulate cortex. The lesioned animals did not show decreased LCBF in MPFC per se. D1 and D2 DA receptor binding was not affected in any brain region examined. These results suggest that lesions of the DA nerve terminals in MPFC induce an enhancement of functional activity in the terminal regions of the subcortical DA systems, and that hypofunction of the mesocortical dopamine system does not elicit reduced metabolic activity in the prefrontal cortex.

Comparison of effects of bilateral injections of bicuculline and muscimol into the caudate-putamen of amygdaloid-kindled rats

Bicuculline is an antagonist of gamma-aminobutyric acid (GABA) receptors, and muscimol is an agonist of GABA receptors. In this study, the effects of bilateral injections of bicuculline and muscimol into the caudate-putamen (CP) were compared in amygdaloid-kindled rats. Thirty minutes after the injection of bicuculline (1, 10 and 100 pmol per CP) or muscimol (10, 50 and 100 nmol per CP), the kindled amygdala was stimulated at the previously established generalized seizure triggering threshold (GST). Most doses of bicuculline caused no significant alteration either in the seizure stage or in the afterdischarge duration. Only the 100-pmol dose produced a marked reduction in the afterdischarge duration. With 10 nmol of muscimol, there was no significant change in the kindled seizure stage or in the afterdischarge duration. However, 50 and 100 nmol of muscimol markedly suppressed both parameters. These findings suggest that CP efferent pathways are involved in the mechanism that underlies the development of kindled amygdaloid seizures, and support the concept that GABA acts as an anticonvulsant in the brain.

Rolling mouse Nagoya as a mutant animal model of basal ganglia dysfunction: determination of absolute rates of local cerebral glucose utilization

In order to elucidate the neuronal mechanism of the motor disturbances of the Rolling mouse Nagoya (rolling), a neurological mutant mouse (genotype rol/rol) showing frequent lurching and falling over on walking, we determined absolute rates of local cerebral glucose utilization (LCGU) with the [14C]deoxyglucose method. The rates were compared with those of heterozygote (+/rol) with normal behavior, and of normal mice (+/+) of the same strain (C3Hf/Nga). Rolling showed marked and significant increases in LCGU in the structures of the basal ganglia such as the globus pallidus, entopeduncular nucleus, substantia nigra pars compacta and pars reticulata, and subthalamic nucleus, confirming our previous finding with semiquantitative LCGU determination. Additional significant but much less marked increases in LCGU of rolling were found in some structures of the brainstem and limbic system, such as the pedunculopontine nucleus, red nucleus, ventral tegmental area, lateral habenula, and CA1 and CA3 of the hippocampus. Although rolling has been regarded as an animal model of cerebellar ataxia, rolling showed no alterations of LCGU in the cerebellum. The heterozygote showed intermediate increases in LCGU between rolling and normal mice in the basal ganglia structures such as the globus pallidus, substantia nigra pars reticulata and subthalamic nucleus. Our findings indicate that rolling has a definite, genetically determined dysfunction of the basal ganglia. The primary site of the basal ganglia dysfunction might probably be in the striatum, involving both the neostriatum and limbic striatum, and resulting in secondary dysfunction in their target structures.

Striatal dopamine in motor activation and reward-mediated learning: steps towards a unifying model

On the basis of behavioural evidence, dopamine is found to be involved in two higher-level functions of the brain: reward-mediated learning and motor activation. In these functions dopamine appears to mediate synaptic enhancement in the corticostriatal pathway. However, in electrophysiological studies, dopamine is often reported to inhibit corticostriatal transmission. These two effects of dopamine seem incompatible. The existence of separate populations of dopamine receptors, differentially modulating cholinergic and glutamatergic synapses, suggests a possible resolution to this paradox. The synaptic enhancement which occurs in reward-mediated learning may also be involved in dopamine-mediated motor activation. The logical form of reward-mediated learning imposes constraints on which mechanisms can be considered possible. Dopamine D1 receptors may mediate enhancement of corticostriatal synapses. On the other hand, dopamine D2 receptors on cholinergic terminals may mediate indirect, inhibitory effects of dopamine on striatal neurons.

Progressive pathology of the caudate nucleus, the substantia nigra pars reticulata and the deeper layers of the colliculus superior: acute behavioural and metabolic effects of intrastriatal kainic acid

The acute behavioural and metabolic consequences of functional changes following unilateral intracaudate kainic acid at the level of the feline caudate nucleus, the substantia nigra pars reticulata and the deeper layers of the colliculus superior were investigated. The present study became possible since it was previously found that unilateral changes in neurotransmission processes in these structures all result in behavioural alterations that can be distinguished from each other. During the first 17 min after kainic acid, all animals displayed contralateral forced staccato head turning; these movements are characteristic for an activation of dopamine receptors and/or inhibition of GABA receptors in the rostromedial caudate nucleus. Between 15 and 50 min, all animals displayed fast, uninterrupted contralateral forced head, torso or body turning; these movements are characteristic for an activation of nigral GABA receptors. From about 48 min, all animals displayed sequences of short contralateral forced ear, head, torso and body turnings; these movements are characteristic for an inhibition of collicular GABA receptors. Furthermore, most cats displayed ipsilateral orofacial dyskinetic movements during the whole 180 min observation period. Metabolism was analysed in three cats that received [14C]2-D-deoxyglucose immediately before, 5 min after, or 70 min after kainic acid. Metabolism was increased in the ipsilateral caudate nucleus; this effect was most pronounced in the cat that received deoxyglucose immediately before kainic acid. Metabolic activity was increased in the ipsilateral substantia nigra pars reticulata; this effect was most pronounced in the cat treated with deoxyglucose 5 min after kainic acid. Metabolism was increased in the ipsilateral deeper layers of the colliculus superior in the cat that received deoxyglucose 70 min after kainic acid. The present behavioural and metabolic data suggest that kainic acid produces an increasing pathology resulting successively in functional changes in the caudate nucleus, its output-station the substantia nigra pars reticulata and the nigral output-station the deeper layers of the colliculus superior. It is suggested that the successive appearance of the latter effects is inherent in the hierarchical order of the brain structures under study. The occurrence of orofacial dyskinetic movements during the whole observation period suggests that the former movements were not mediated via the striato-nigro-collicular pathway. Finally, apomorphine injected in the ipsilateral caudate nucleus 1 week after kainic acid was significantly less effective compared to apomorphine injected 1 week before kainic acid. The c